WO 20011/101019 A1 describes a impeller-type coolant pump with an outlet valve arrangement in the root of an outlet channel. The output valve arrangement is provided with a valve flap, whereby the pivot axis of the valve flap is arranged at one end of the flap body and is provided in the surface plane of the outlet channel. The valve flap must be pivotable even at high rotational speeds of the pump rotor at which a high fluid pressure against the valve flap either in closing direction or in opening direction can occur. High actuation power is, however, needed to provide full functionality at all rotational speeds.